Recently, nucleoprotein complexes (NPCs) have been isolated from Simian Virus 40 and Polyoma virus virions and from cells infected with these viruses. The proteins of these viral DNA-protein complexes have been identified as host cell histones. The close association of papovavirus DNA and host histones suggests that histones may function in controlling papovavirus DNA structure and/or expression. Consequently, this research proposal is designed to investigate the relationship of cellular histones to the superhelix density of papovavirus DNA. Current experiments are aimed at accurately determining the histone content of natural pavovavirus NPCs from virions and virus infected cells. In addition, similar determinations are being performed with viral NPCs extracted from cells which have been treated with cycloheximide, or canavanine and from cells which are arginine deprived. Under these conditions it is anticipated that protein (histone) synthesis will be inhibited and that less histone will be bound to viral DNA. Numerous reports have shown that inhibition of protein synthesis in papovavirus infected cells leads to a reduction in superhelix density of the DNA. Thus, if less histone is present on the NPCs and the superhelix density of their DNA is decreased, some indirect evidence for a relationship between histones and viral DNA structure will have been demonstrated. More direct evidence will be obtained by actually forming NPCs in vitro using viral DNA and various concentrations of purified histones.